1. Field of Invention
The invention relates to an ink set for inkjet recording.
2. Description of the Related Art
Inkjet recording performs recording by jetting ink droplets from each of a number of nozzles formed on an inkjet head. The method is widely used because the noise during a recording operation is low, running costs are low, and a high quality image can be recorded on a wide variety of recording media.
A two-liquid reaction process is known as one employable an inkjet recording method. The two-liquid reaction process involves reacting an ink and a reaction liquid which coagulates the ink with each other so as to coagulate the ink and thus accelerate ink fixation.
Examples of the inkjet recording method using the two-liquid reaction process include an inkjet recording method described in JP-A No. 2005-74654. In this method, the surface tension of a reaction liquid containing a zirconium salt and an ammonium salt is set to be higher than the average value of the surface tensions of aqueous pigment inks used in combination with the reaction liquid, the surface tension of the reaction liquid is from 25 to 50 mN/m, the surface tensions of the inks are from 20 to 50 mN/m, and the difference between the surface tension of the reaction liquid and the average of the surface tensions of the inks is in a range of from 5 to 25 mN/m. This inkjet recording method is taught as providing high image density and excellent rub-fastness without bleedings.
Examples of the inkjet recording method using the two-liquid reaction process further include an image forming method described in JP-A No. 2007-331171. This method includes a process of forming a film of an aggregate on the surface of a reaction liquid existing in liquid form, the aggregate film being formed by aggregation of a pigment aggregate generated by ejecting an ink having low surface tension onto a reaction liquid having high surface tension and contacting the ink with the reaction liquid, and in which inks are applied in order of decreasing surface tension.
Conventionally, with a two-liquid ink set for inkjet recording using an ink composition and a reaction liquid, an image is obtained by coagulating the ink using the reaction liquid. It is necessary to evenly apply the reaction liquid to the recording medium as a single liquid before the ink is applied to the recording medium. Further, it is desirable that the applied reaction liquid functions effectively and without waste with respect to coagulation of the ink. Coating of a reaction liquid on a recording medium is performed such that the coating liquid is applied to the recording medium to a thickness of from one to several microns; however, it is difficult to form a uniform image because of problems such as the occurrence of reticulated irregularities when the liquid is coated on the recording medium from a coating roller or penetration of the coated reaction liquid into the base layer of the paper, as a result of which the reactant included in the reaction liquid does not function sufficiently as a coagulant.